Deflake FrameMetricsListenerTest

Sometimes the GPU duration can be zero if, for instance, a frame
dropped, or if GPU work completed so quickly it outran the estimated
start timepoint on the CPU. HWUI will try to clamp to ensure that the
GPU duration is nonnegative, but the test should allow for occasional
zero-durations.

Bug: 230713131
Bug: 240888213
Test: FrameMetricsListenerTest
Change-Id: I70eee2dbbc73f22a9136ca9a09986f37c0595651
Merged-In: I70eee2dbbc73f22a9136ca9a09986f37c0595651
(cherry picked from commit 8c8a4329c20362f30cc4c4c8f04c999f8cf2ba8d)